Tubes for yarn bobbins are devices comprising a perforated cylindrical or frusto-conical surface for retaining the yarn reeled on the tube while said yarn is exposed to a liquid treatment, especially a dyeing with a subsequent drying, in an apparatus in which several tubes are located end to end on perforated distributor pipes through which the treatment liquid is pumped out through the yarn.
The present invention and the prior art will be described below with reference to cylindrical tubes as a conical shape of the tube does not change the problems with which the invention is concerned, viz. the problems arising in connection with the liquid treatment, but which shape is substantially used for the sake of rewinding the yarn.
Tubes for yarn bobbins must especially meet the following three requirements:
1. They must be inexpensive because they are employed in a very high number, which to a single dye-works may be of the magnitude 1/2 million. PA0 2. They must permit the densest possible filling of yarn bobbins in the dyeing apparatus to minimize the consumption of water and chemicals, especially to avoid pollution of the environment with the waste liquids. PA0 3. They must permit a uniform dyeing and drying of the yarn.
The oldest known tube which is used today is a perforated metal cylinder. Tubes of this type are placed on the distributor pipes with discs between every two tubes and are compressed by means of a cap screwed on the end of the distributor pipe, thus providing a seal between the metal cylinder and the intermediary discs. These tubes provide the most uniform dyeing of yarn, but they have the disadvantage that they are rather expensive and allow only a very bad filling of the space in the dyeing apparatus, partly because the intermediary discs take up room and partly because the tubes do not permit a compression of the yarn bobbins. In fact these tubes permit a filling of the yarn dyeing apparatus which is only well over half of what can be obtained with certain other types of tubes.
Therefore tubes have been produced of variable length in axial direction, so that the yarn bobbin can be compressed. Such a tube may for instance be a compressible metal spiral or two metal cages displaceable relative to each other and locked together with a ring, and which are kept in a stretched position by a helical spring as described in U.S. Pat. No. 2,818,222. This type of tubes permits a good filling of the space in the dyeing apparatus, but is expensive due to the nature of the material since in practice only stainless steel can be used, and such tubes give rise to uneven dyeing.
A second type of tubes of variable length in axial direction is the type disclosed in British Patent specification No. 1,169,962, and it is made of an injection moulded plastic material in which the cylinder surface is formed by a row of concentric rings connected by strings extending obliquely relative to the axial direction and being of such dimensions that the tube may be compressed in the axial direction by virtue of the resilience of the material. These tubes have the advantage to be very inexpensive, but are in practice only disposable tubes because the plastic material undergoes a heat set at the high temperatures used for dyeing and drying, and therefore the tubes are either to be discarded or to be straightened again after every use after being heated in hot-air. Furthermore it is not possible either by the use of these tubes to obtain a desired uniformity of the dyeings.
The cause of the uneven dyeing when using the known tubes of variable length has turned out to be the fact that no efficient seal exists between two adjacent bobbins in spite of the compression thereof. This has the effect that a large part of the circulating amount of dye liquid takes the easier path betwen two bobbins instead of passing through the bobbins. In practice this is a major drawback since the amount of dye liquid passing between the bobbins is uncontrollable. Measurings have shown that at lower temperatures minimum amounts of from 0 to 20% pass, but this only applies as long as the yarn is resilient, whereby the compression of the bobbins assist in forming a seal. As the resilience of the yarn decreases during the influence of heat, the amount of dye liquid passing between two bobbins increases. The mean value of the measurings is 50% dye liquid, and in extreme cases 80 to 90% may be measured. These figures apply to yarn of wool/acryl mixtures at temperatures of 40.degree. to 100.degree. C. When after a completed process yarn and dye liquid are cooled, the yarn bobbins and the fixed tubes shrink, whereby the leaks and consequently the flow losses are increased. A tube, which for instance is fixed in a length of 100 mm at 100.degree. C., shrinks 1.25 mm at cooling to 30.degree. C. Thus after the cooling a space of 1.25 mm is present between two adjacent bobbins. The result is uneven dyeings, especially in cases where after completed dyeing and shade control it is found necessary to cool the dye in order to add more dyestuff. By this shading process large flow losses occur during the entire rise of temperature because the channels in the yarn formed during the first dyeing are permanent and cannot even be removed by an increased compression of the bobbins. The same leaks also exist during the drying when hot air in large amounts is blown through the bobbins. This causes longer drying periods and a heavy loss of energy.
This drawback may be overcome by the two end rings being differently shaped and with such profiles that one end ring presents an outer cylinder or conical surface fitting in an inner cylinder or concical surface on the second ring, and by both rings being provided with an outward radial flange, cf. British Patent specification No. 1,333,608. In this manner a uniform dyeing and drying of yarn is obtained, the seal between the tubes not depending on an axial compression of the tubes end to end, but being established by virtue of the seal between the two cylinder or conical surfaces of the end rings. However, the tube according to British Patent specification No. 1,333,608 is encumbered with the same drawbacks as the tube according to British Patent specification No. 1,169,962, as the strings extending between the concentric rings are the supporting means for the yarn reeled, for which reason they must possess such a strength and thickness that the tube is difficult to restraighten after use due to the heat set of the plastic material. Furthermore, the strings must extend obliquely relative to the axial direction and therefore in a direction substantially parallel to the winding line of the yarn, whereby the inner yarn layer may get jammed at the compression of the tube, which in practice may cause a waste of yarn of 1 to 1.5%.